U.S. patent application number 16/976603 was filed with the patent office on 2021-02-18 for polishing composition and polishing method using the same.
This patent application is currently assigned to FUJIMI INCORPORATED. The applicant listed for this patent is FUJIMI INCORPORATED. Invention is credited to Tzu-Chun TSENG.
Application Number | 20210047541 16/976603 |
Document ID | / |
Family ID | 1000005224207 |
Filed Date | 2021-02-18 |
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United States Patent
Application |
20210047541 |
Kind Code |
A1 |
TSENG; Tzu-Chun |
February 18, 2021 |
POLISHING COMPOSITION AND POLISHING METHOD USING THE SAME
Abstract
Provided is a polishing composition that allows carbon-added
silicon oxide (SiOC) to be polished at a higher polishing speed
than the polishing speed of silicon nitride (i.e., the selection
ratio of SiOC/silicon nitride is high). A polishing composition
containing spinous silica particles and a dispersing medium, in
which the pH is less than 5.
Inventors: |
TSENG; Tzu-Chun; (Tongluo
Township, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIMI INCORPORATED |
Kiyosu-shi, Aichi |
|
JP |
|
|
Assignee: |
FUJIMI INCORPORATED
Kiyosu-shi, Aichi
JP
|
Family ID: |
1000005224207 |
Appl. No.: |
16/976603 |
Filed: |
March 13, 2019 |
PCT Filed: |
March 13, 2019 |
PCT NO: |
PCT/JP2019/010307 |
371 Date: |
August 28, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C01B 33/12 20130101;
H01L 21/3212 20130101; C09G 1/02 20130101 |
International
Class: |
C09G 1/02 20060101
C09G001/02; H01L 21/321 20060101 H01L021/321; C01B 33/12 20060101
C01B033/12 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 20, 2018 |
JP |
2018-053106 |
Claims
1. A polishing composition comprising: spinous silica particles;
and a dispersing medium, wherein a pH is less than 5.
2. The polishing composition according to claim 1, wherein the
silica particles are cation-modified silica particles.
3. The polishing composition according to claim 2, wherein the
cation-modified silica particles are amino group-modified silica
particles.
4. The polishing composition according to claim 1, wherein a pH is
2 or more and 4 or less.
5. The polishing composition according to claim 1, wherein the
polishing composition is used for a step of polishing an object to
be polished containing carbon-added silicon oxide and silicon
nitride.
6. A polishing method comprising the step of polishing an object to
be polished by using the polishing composition according to claim
1.
7. The polishing method according to claim 6, wherein the object to
be polished contains carbon-added silicon oxide and silicon
nitride.
8. A method of producing a semiconductor substrate, comprising the
step of polishing an object to be polished by the polishing method
according to claim 6.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polishing composition and
a polishing method using the polishing composition.
BACKGROUND ART
[0002] In recent years, a so-called chemical mechanical polishing
(CMP) technique for physically polishing and flattening a
semiconductor substrate in producing a device have been used in
association with multilayer wiring on a surface of a semiconductor
substrate. CMP is a method for flattening a surface of an object to
be polished (polishing object) such as a semiconductor substrate by
using a polishing composition (slurry) containing abrasive grains
such as silica, alumina, or ceria, an anti-corrosion agent, a
surfactant, or the like. CMP is specifically used in processes such
as shallow trench isolation (STI), flattening of interlayer
insulating films (ILD films), formation of tungsten plugs, and
formation of multilayer interconnections composed of copper and a
low dielectric film. In such a CMP, in the case of an STI process
or the like, it has been desired that a first insulating film
(e.g., carbon-added silicon oxide (SiOC) film) and a second
insulating film (e.g., silicon nitride film) are polished and
removed at a high polishing selection ratio (i.e., removing the
SiOC film at a higher polishing speed than the polishing speed of
the silicon nitride film).
[0003] As a technique described above, Japanese Patent Application
Publication No. 2006-203188 discloses that the polishing speed of
an insulating film (silicon nitride film, SiOC film or the like) is
improved by using a chemical mechanical polishing composition
containing methanesulfonic acid, an alkali metal ion, an oxidizing
agent, and a silica polishing agent.
SUMMARY OF INVENTION
[0004] However, when a polishing composition as described in
Japanese Patent Application Publication No. 2006-203188 is used to
polish an object to be polished containing silicon nitride and
carbon-added silicon oxide (SiOC), SiOC and silicon nitride are
both polished at a high speed, and therefore a high polishing
selection ratio of SiOC to silicon nitride cannot be obtained.
[0005] The present invention is conceived in light of the above
problems, and an object of the present invention is to provide a
polishing composition in which the polishing speed of SiOC is
sufficiently high relative to the polishing speed of silicon
nitride (i.e., the selection ratio of SiOC/silicon nitride is
high).
[0006] In light of the above problems, the inventors of the present
invention conducted intensive studies. As a result, the inventors
of the present invention found that the above-described problems
can be solved by using a polishing composition which contains
spinous silica particles and a dispersing medium, and in which the
pH is less than 5, and completed the present invention
accordingly.
BRIEF DESCRIPTION OF DRAWINGS
[0007] FIG. 1 is a drawing illustrating spinous silica particles in
an embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
[0008] Hereinafter, the present invention will be described. Note
that, the present invention is not limited to the following
embodiments.
[0009] Incidentally, in the present specification, the term
"(meth)acryl" in the specific name of a compound inclusively means
"acryl" and "methacryl", and "(meth)acrylate" inclusively means
"acrylate" and "methacrylate". Furthermore, "X to Y" indicating a
range means "X or more and Y or less", and "ppm", "%", and "parts",
respectively mean "mass parts per million", "mass %", and "parts by
mass". Further, unless otherwise noted, operations and measurement
of physical properties or the like are performed under conditions
at room temperature (20 to 25.degree. C.) and a relative humidity
of 40 to 50% RH.
[0010] The polishing composition according to the present invention
is expected to be also effective for objects to be polished other
than the object to be polished containing SiOC and silicon nitride.
For example, the polishing composition according to the present
invention is also expected to be effective for an object to be
polished containing, for example, a silicon oxide film formed from
TEOS as a raw material. Here, from the viewpoint of effects
provided by the present invention, the polishing composition
according to an embodiment of the present invention is preferably
used in a process of polishing an object to be polished containing
SiOC and silicon nitride. This is because, in such an object to be
polished, the polishing selection ratio is presumably increased due
to the mechanism described later.
[0011] The inventors of the present invention presume a mechanism
to solve the above-described problems by the present invention as
follows. Note that the following mechanism is only a presumption,
and the scope of the present invention is not limited by this
mechanism.
[0012] The polishing composition according to the present invention
contains spinous silica particles and a dispersing medium, and the
pH thereof is less than 5. In a case where the pH is less than 5,
the surfaces of silicon nitride (isoelectric point is approximately
less than 5) and silica particles are positively charged, and the
surface of SiOC is negatively charged. Thus, it is conceived that
SiOC and silica particles are adsorbed to each other, whereby the
polishing speed of SiOC is increased, whereas silicon nitride and
silica particles repulse against each other, whereby the polishing
speed of silicon nitride is decreased, and, as a result, polishing
in which the polishing speed of SiOC is sufficiently high relative
to the polishing speed of silicon nitride could be achieved.
Further, in the polishing composition according to the present
invention, the surface morphology of silica particles has to be a
spinous shape. Although the mechanism thereof is not clear, in a
case where spinous silica particles are used, the polishing speed
of SiOC is improved and the polishing speed of silicon nitride does
not significantly change compared to a case where silica particles
having a smooth surface are used. Thus, a high selection ratio of
SiOC/silicon nitride can be achieved. That is, according to the
present invention, a polishing composition in which the polishing
speed of SiOC is sufficiently high relative to the polishing speed
of silicon nitride (i.e., the selection ratio of SiOC/silicon
nitride is high) is provided.
[0013] (Spinous Silica Particles)
[0014] In the present specification, the term "spinous silica
particle" refers to a silica particle having a plurality of
protrusions on particle surface. Incidentally, the term "spinous
silica particle" is also simply referred to as "silica particle" as
below. In one or a plurality of embodiments, the spinous silica
particles have a shape in which, based on the particles size of the
smallest silica particle, two or more particles whose particle size
are different five times or more are aggregated or fused. Among two
or more particles whose particle sizes are different five times or
more, a small particle is preferably partially embedded in a large
particle. In a case where such spinous silica particles are used,
the polishing speed of SiOC is improved and the polishing speed of
silicon nitride does not significantly change compared to a case
where silica particles having a smooth surface are used, and
therefore a high selection ratio of SiOC/silicon nitride can be
achieved.
[0015] Here, examples of the spinous silica particle include
spinous colloidal silica, and spinous fumed silica. From the
viewpoint of suppressing generation of polishing scratch, spinous
colloidal silica is preferred.
[0016] (Method of Producing Spinous Silica Particles)
[0017] Silica particles having a plurality of protrusions on the
surface thereof, that is, spinous silica particles can be produced,
for example, by the following method.
[0018] First, alkoxysilane is continuously added to a mixed
solution of methanol and water in which ammonia aqueous solution
has been added as a catalyst to perform hydrolysis, and thereby a
slurry containing colloidal silica particles is obtained. The
obtained slurry is heated to distill off methanol and ammonia.
Then, an organic alkali as a catalyst is added to the slurry, and
alkoxysilane is continuously added again thereto at a temperature
of 70.degree. C. or higher to perform hydrolysis, thus forming a
plurality of protrusions on the surface of colloidal silica
particles. Specific examples of the organic alkali that can be used
herein include amine compounds such as triethanolamine, and
quaternary ammonium compounds such as tetramethyl ammonium
hydroxide. With this method, silica particles in which the content
of metal impurities is 1 mass ppm or less and which has a plurality
of protrusions on the surface thereof can be easily obtained.
Further, in the later description, this production method may be
referred to as "production method A".
[0019] Note that a general method of producing colloidal silica
through hydrolysis of alkoxysilane is described in, for example,
"Science of Sol-Gel Method", written by Sumio Sakuka (Agne Shofu
Publishing Inc.), pp. 154 to 156. Japanese Patent Application
Publication No. H11-60232 also discloses a method of producing
cocoon-shaped colloidal silica, the method including adding
dropwise methyl silicate or a mixture of methyl silicate and
methanol to a mixed solvent containing water, methanol, and
ammonia, or ammonia and an ammonium salt, thus reacting methyl
silicate with water. Japanese Patent Application Publication No.
2001-48520 discloses a method of producing elongated colloidal
silica, the method including hydrolyzing alkylsilicate with an acid
catalyst, then adding an alkali catalyst thereto, and heating the
mixture to proceed polymerization of silicic acid, thus growing
particles. Japanese Patent Application Publication No. 2007-153732
describes a method of producing a colloidal silica having many
small protrusions by using a specific amount of a specific type of
hydrolysis catalyst and using readily hydrolyzable organosilicate
as a raw material. Japanese Patent Application Publication No.
2002-338232 describes a method of producing secondary aggregated
colloidal silica, the method including adding a flocculant to
monodispersed colloidal silica, thus causing the colloidal silica
particles to be secondarily aggregated into spherical shapes.
Japanese Patent Application Publication No. H07-118008 and
International Patent Application Publication No. 2007/018069
disclose that calcium salt or magnesium salt is added to active
silicic acid obtained from sodium silicate to obtain heteromorphic
colloidal silicas such as elongated colloidal silica. Japanese
Patent Application Publication No. 2001-11433 describes that
moniliform colloidal silica is obtained by adding calcium salt to
active silicic acid obtained from sodium silicate. Japanese Patent
Application Publication No. 2008-169102 descries that colloidal
silica having many small protrusions like konpeito (Japanese
confetti) is obtained by forming and growing microparticles on the
surface of seed particles. The spinous silica particles according
to the present invention can also be produced by using the method
described in these literatures singly or in combination.
[0020] Note that the presence or absence of respective protrusions
of spinous silica particles can be observed by a scanning electron
microscope.
[0021] The number of protrusions of the surface of spinous silica
particle is preferably 3 or more, and more preferably 5 or more,
per particle on average.
[0022] The protrusion herein is a protrusion having sufficiently
small height and width compared to the particle size of the spinous
silica particle. More specifically, a protrusion is such that the
length of a portion shown in FIG. 1 as a curve AB which passes
through a point A and a point B does not exceed one-fourth of the
circumferential length of the maximum inscribed circle of the
spinous silica particle, or more accurately, the circumferential
length of the maximum circle inscribed in a projected contour of
the outer shape of the spinous silica particle. Note that the width
of the protrusion refers to the width of the base portion of the
protrusion, and is represented as the distance between the point A
and the point B in FIG. 1. The height of the protrusion refers to
the distance between the base portion of the protrusion and a
portion of the protrusion furthest from the base portion, and is
expressed in FIG. 1 as the length of a segment CD which is
orthogonal to a straight line AB.
[0023] The average of values obtained by dividing the height of the
protrusions of the surface of spinous silica particles by the width
of the base portion in corresponding protrusions (height of
protrusion/width of protrusion) is preferably 0.170 or more, more
preferably 0.200 or more, and even more preferably 0.220 or more.
As the average of the values increases, the polishing speed with
the polishing composition is improved because the shapes of the
protrusions are comparatively sharp. Note that, the height of each
protrusion and the width of base portion of each protrusion of the
spinous silica particle can be determined by analyzing an image of
the spinous silica particle observed by a scanning electron
microscope using a common image analysis software.
[0024] The average height of protrusions of the surface of the
spinous silica particle is preferably 3.5 nm or more, more
preferably 4.0 nm or more, and even more preferably 5.0 nm or more.
As the average height of protrusions increases, the polishing speed
of SiOC by the polishing composition is improved.
[0025] The lower limit of the average primary particle size of the
spinous silica particle is preferably 10 nm or more, more
preferably 15 nm or more, and even more preferably 20 nm or more.
Further, the upper limit of the average primary particle size of
the spinous silica particle is preferably 200 nm or less, more
preferably 150 nm or less, and even more preferably 100 nm or less.
Within such a range, the polishing speed of an object to be
polished (SiOC) by the polishing composition is improved, and
defects generated on the surface of the object to be polished after
polishing with the polishing composition can be suppressed. Note
that the average primary particle size of the spinous silica
particle is calculated based on, for example, the specific surface
area of the spinous silica particle measured by the BET method.
[0026] The lower limit of the average secondary particle size of
the spinous silica particle is preferably 15 nm or more, more
preferably 20 nm or more, and even more preferably 30 nm or more.
Further, the upper limit of the average secondary particle size of
the spinous silica particle is preferably 300 nm or less, more
preferably 260 nm or less, even more preferably 220 nm or less,
particularly preferably 150 nm, and particularly preferably 100 nm
or less. Within such a range, the polishing speed of an object to
be polished (SiOC) by the polishing composition is improved, and
defects generated on the surface of the object to be polished after
polishing with the polishing composition can be suppressed.
Incidentally, the secondary particle herein refers to a particle
formed by the association of spinous silica particles in the
polishing composition. The average secondary particle size of these
secondary particles (average secondary particle size) can be
measured by, for example, a dynamic light scattering method.
[0027] In the polishing composition according to the present
invention, the content (concentration) of the spinous silica
particles is not particularly limited. The content of the spinous
silica particles is preferably 1 mass % or more, more preferably 2
mass % or more, and even more preferably 3 mass % or more relative
to the amount of the polishing composition. The polishing speed of
SiOC tends to be further increased with increase in the content of
spinous silica particles. Further, from the viewpoint of preventing
scratch or the like, usually, the content of the spinous silica
particles is suitably 20 mass % or less, preferably 15 mass % or
less, and more preferably 10 mass % or less. A small content of
spinous silica particles is preferred from the viewpoint of
economic efficiency.
[0028] (Cation-Modified Silica Particles)
[0029] In the present invention, spinous silica particles may be
modified with cation. The reason for this is as follows. In a case
where the pH is less than 5, the surface of SiOC is negatively
charged, and the surface of normal silica particles is positively
charged, whereby SiOC and silica particles are adsorbed to each
other. As a result, the polishing speed of SiOC is increased. On
the contrary, silicon nitride is positively charged, whereby
silicon nitride and silica particles repulse against each other. As
a result, the polishing speed of silicon nitride is decreased.
Here, in order to further enhance an adsorption force or a
repulsive force between spinous silica particles and objects to be
polished, the inventors of the present invention modified the
surface of spinous silica particle with cation to introduce a
positive (+) charge, and thus obtained cation-modified silica
particles in which the positive absolute value of zeta potential is
large under the condition that the pH is less than 5. That is, in
the present invention, (spinous) cation-modified silica particles
are preferably used. The cationic modification herein refers to a
state in which a cation group (e.g., an amino group or a quaternary
cation group) is bonded to the surface of silica particle.
According to a preferred embodiment of the present invention, the
cation-modified silica particle is an amino group-modified silica
particle. According to such an embodiment, the effect of polishing
with a high selection ratio of SiOC/silicon nitride can be
enhanced.
[0030] Herein, the term "zeta (.zeta.) potential" refers to a
difference in electric potential occurred in the interface between
a solid and a liquid when the solid and the liquid in contact with
each other relatively move. In a case where the pH is less than 5,
silicon nitride and silica particles are similarly positively
charged. Thus, when a difference in absolute value of zeta
potential between silicon nitride and silica particles increases,
the repulsion between silicon nitride and silica particles is
strong, and the polishing speed is decreased. The difference in
absolute value of zeta potential of silicon nitride and silica
particles is not particularly limited, but is preferably 1 mV or
more, more preferably 5 mV or more, and even more preferably 10 mV
or more. On the contrary, SiOC is negatively charged. Thus, as a
difference in the absolute value of zeta potential between SiOC and
silica particles is increased, SiOC and silica particles become
easy to contact, and the polishing speed is increased. The
difference in absolute value of the zeta potential of SiOC and
silica particles is not particularly limited, but is preferably 10
mV or more, more preferably 15 mV or more, and even more preferably
20 mV or more.
[0031] Here, spinous silica particles can be modified with cations
by adding a silane coupling agent having a cation group to spinous
silica particles, and allowing them to react at a predetermined
temperature for a predetermined period of time.
[0032] The silane coupling agent used at that time is not
particularly limited. Example thereof include
N-(.beta.-aminoethyl)-.gamma.-aminopropylmethyldimethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropyltriethoxysilane,
.gamma.-aminopropyltriethoxysilane((3-aminopropyl)triethoxysilane),
.gamma.-aminopropyltrimethoxysilane,
.gamma.-triethoxysilyl-N-(.alpha.,.gamma.-dimethyl-butylidene)propylamine-
, N-phenyl-.gamma.-aminopropyltrimethoxysilane,
N-(vinylbenzyl)-.beta.-aminoethyl-.gamma.-aminopropyltriethoxysilane
hydrochloride,
octadecyldimethyl-(.gamma.-trimethoxysilylpropyl)-ammonium chlorid
and the like. Among these, from the viewpoint of favorable
reactivity with colloidal silica,
N-(.beta.-aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropyltriethoxysilane,
.gamma.-aminopropyltriethoxysilane, or
.gamma.-aminopropyltrimethoxysilane is preferably used. Note that,
in the present invention, one type of silane coupling agent may be
used singly, or two or more types thereof may be used in
combination.
[0033] Note that the silane coupling agent can be added to silica
particles directly or by diluting with a hydrophilic organic
solvent. By diluting the silane coupling agent with the hydrophilic
organic solvent, production of aggregates can be suppressed. In a
case where the silane coupling agent is diluted with a hydrophilic
organic solvent, the silane coupling agent may be diluted with
preferably 5 parts by mass or more and 50 parts by mass or less, or
more preferably 10 parts by mass or more and 20 parts by mass or
less of the hydrophilic organic solvent, per 1 part by mass of the
silane coupling agent (in the case of containing two types or more,
the total amount thereof). The hydrophilic organic solvent is not
particularly limited, and examples thereof include lower alcohols
such as methanol, ethanol, isopropanol, butanol, and the like.
[0034] Further, it is conceived that, by adjusting the pH of raw
material silica and the amount of the silane coupling agent added,
the amount of cation group introduced to the surface of silica
particles can be adjusted. The amount of silane coupling agent used
is not particularly limited, and the amount is preferably 0.01 mass
% or more and 3.0 mass % or less, and more preferably approximately
0.05 mass % or more and 1.0 mass % or less relative to silica
particles.
[0035] The treatment temperature for cationic modification of
silica particles with a silane coupling agent is not particularly
limited, and needs to be from room temperature (e.g., 25.degree.
C.) to around the boiling point of a dispersing medium to disperse
silica particles. Specifically, the treatment temperature is
0.degree. C. or higher and 100.degree. C. or lower, and preferably
around room temperature (e.g., 25.degree. C.) or higher and
90.degree. C. or lower.
[0036] (pH)
[0037] The pH of the polishing composition according to the present
invention is less than 5. As described above, it is conceived that,
in a case where the pH is less than 5, the surfaces of silicon
nitride and silica particles are positively charged, and the
surface of SiOC is negatively charged, whereby SiOC and silica
particles are adsorbed to each other, resulting in increase in the
polishing speed of SiOC, whereas silicon nitride and silica
particles repulse against each other, resulting in decrease in the
polishing speed of silicon nitride, and as a result, polishing, in
which the polishing speed of SiOC is sufficiently high relative to
the polishing speed of silicon nitride, could be achieved. In a
preferred embodiment, the pH of the polishing composition is 4.5 or
less, more preferably 4 or less, and even more preferably 3.8 or
less.
[0038] The lower limit of the pH of the polishing composition is
not particularly limited, but is preferably 1 or more, more
preferably 1.5 or more, even more preferably 2 or more,
particularly preferably 2.5 or more, and most preferably 3 or more,
from the perspectives of facilitating handling, and improving the
polishing speed of SiOC and the selection ratio of SiOC/SiN.
[0039] For example, in a preferred embodiment, the pH of the
polishing composition is 2 or more and 4 or less.
[0040] A pH adjusting agent is used for adjusting the pH of the
polishing composition of the present invention.
[0041] As the pH adjusting agent, a publicly known acid, a base, or
salts thereof can be used.
[0042] Specific examples of the acid that can be used as the pH
adjusting agent include, for example, inorganic acids such as
hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid,
boric acid, carbonic acid, hypophosphorous acid, phosphorous acid,
and phosphoric acid; and organic acids such as formic acid, acetic
acid, propionic acid, butyric acid, valeric acid, 2-methylbutyric
acid, n-hexanoic acid, 3,3-dimethylbutyric acid, 2-ethylbutyric
acid, 4-methylpentanoic acid, n-heptanoic acid, 2-methylhexanoic
acid, n-octanoic acid, 2-ethylhexanoic acid, benzoic acid, glycolic
acid, salicylic acid, glyceric acid, oxalic acid, malonic acid,
succinic acid, glutaric acid, adipic acid, pimelic acid, maleic
acid, phthalic acid, malic acid, gluconic acid, itaconic acid,
tartaric acid, citric acid, lactic acid, diglycolic acid,
2-furancarboxylic acid, 2,5-furandicarboxylic acid,
3-furancarboxylic acid, 2-tetrahydrofurancarboxylic acid,
methoxyacetic acid, methoxyphenyl acetic acid, phenoxyacetic acid,
and the like. In a case where an inorganic acid is used as the pH
adjusting agent, in particular, sulfuric acid, nitric acid or
phosphoric acid is particularly preferred from the viewpoint of
improving the polishing speed. In a case where an organic acid is
used as the pH adjusting agent, glycolic acid, succinic acid,
maleic acid, citric acid, tartaric acid, malic acid, gluconic acid,
and itaconic acid are preferred.
[0043] Specific examples of the base that can used as the pH
adjusting agent include, for example, amines such as aliphatic
amines, and aromatic amine; organic bases such as quaternary
ammonium hydroxide; hydroxides of alkali metals such as potassium
hydroxide; hydroxides of alkaline earth metals; tetramethyl
ammonium hydroxide; ammonia; and the like. Among these, potassium
hydroxide or ammonia is preferred from the viewpoint of procurement
ease.
[0044] The pH adjusting agent can be used singly or two or more
types thereof may be mixed and used.
[0045] The amount of the pH adjusting agent added is not
particularly limited, and the amount may be appropriately selected
so that the pH is within a target pH range in the present
invention.
[0046] (Dispersing Medium)
[0047] In the polishing composition of the present invention, a
dispersing medium is used for dispersing respective components
constituting the polishing composition. Examples of the dispersing
medium include organic solvents, and water, and among them, the
dispersing medium preferably contains water.
[0048] From the viewpoint of suppressing contamination on an object
to be polished and inhibition to actions of other components, water
that does not contain impurities as much as possible is preferred.
Specifically, deionized water, pure water, or the like is
preferred. Such water can be obtained by, for example, removing
impurity ions with ion exchange resins and then removing foreign
substances through a filter, for example.
[0049] (Polishing Method)
[0050] In the present invention, a polishing method including a
step of polishing a surface of an object to be polished by using
the above-described polishing composition is also provided. The
object to be polished preferably contains SiOC and silicon nitride.
With such a polishing method, SiOC can be selectively polished
relative to silicon nitride.
[0051] A polishing apparatus is not particularly limited, and, for
example, it is possible to use a general polishing apparatus
including a holder for holding a substrate or the like having an
object to be polished, a motor or the like having a changeable
rotation number, and a polishing table to which a polishing pad
(polishing cloth) can be attached.
[0052] As the polishing pad, a general non-woven fabric,
polyurethane, a porous fluororesin, or the like can be used without
any particular limitation.
[0053] The polishing conditions are also not particularly limited.
For example, the rotation speed of a polishing table is preferably
10 rpm or more and 200 rpm or less, the carrier (head) rotation
speed is preferably 10 rpm or more and 200 rpm or less, and the
pressure (polishing pressure) applied to a substrate having an
object to be polished is preferably 0.5 psi or more and 10 psi or
less. A method for supplying a polishing composition to a polishing
pad is not particularly limited. For example, a method in which a
polishing composition is continuously supplied using a pump or the
like can be employed (discarded after single use). The supply
amount is not limited, but a surface of the polishing pad is
preferably covered all the time with the polishing composition of
the present invention.
[0054] (Method of Producing Semiconductor Substrate)
[0055] In the present invention, a method of producing a
semiconductor substrate, including a step of polishing an object to
be polished by the above-described polishing method is also
provided. Since the method of producing a semiconductor substrate
of the present invention includes the above-described polishing
method, SiOC can be selectively polished relative to silicon
nitride, and a semiconductor substrate can be produced according to
the purpose.
EXAMPLES
[0056] The present invention will be described in greater detail
with the following Examples and Comparative Examples. However, the
technical scope of the present invention is not limited only to the
following Examples.
[0057] (Preparation of Polishing Composition)
Example 1
[0058] A colloidal silica dispersion containing 20 mass % of
colloidal silica (spinous shape; colloidal silica produced by the
above-described production method A; primary particle size: 48.4
nm; secondary particle size: 63.1 nm; average height of protrusion:
5.66 nm; and protrusion height/protrusion width=0.25) was prepared
using pure water as a dispersing medium. Then, a polishing
composition was prepared, using nitric acid and pure water, so that
the content of colloidal silica in the polishing composition was
finally 3.2 mass % and the pH was 2.7.
Example 2
[0059] A polishing composition was prepared in the same manner as
in Example 1 except that the pH was adjusted to 3.4.
Example 3
[0060] A colloidal silica dispersion containing 20 mass % of
colloidal silica (spinous shape; and colloidal silica similar to
one of Example 1) was prepared using pure water as a dispersing
medium. To 1 kg of the colloidal silica dispersion, 0.11 g of
(3-aminopropyl)triethoxysilane (APTES) was gradually added (one
drop every approximately 5 seconds, and approximately 0.03 g per
drop). During addition, the colloidal silica dispersion was stirred
with a stirrer at a rate of 300 to 400 rpm. After completion of
addition of APTES, stirring was continued at room temperature
(25.degree. C.) for 5 hours. After completion of stirring, a
mixture of colloidal silica and ATPES was diluted with water, and
the pH value of the resulting mixture was adjusted to 2.6 with
nitric acid. Then, a polishing composition was prepared so that the
content of colloidal silica in the polishing composition was
finally 3.2 mass % and the content of APTES was 17.6 ppm.
Examples 4 to 8
[0061] Polishing compositions of Examples 4 to 8 were prepared in
the same manner as in Example 3 except that the pH was adjusted to
each of the values described in Table 1.
Comparative Example 1
[0062] The polishing composition of Comparative Example 1 was
prepared in the same manner as in Example 1 except that the pH was
adjusted to 5.0.
Comparative Examples 2 to 7
[0063] Polishing compositions of Comparative Examples 2 to were
prepared in the same manner as in Example 3 except that the pH was
adjusted to each of the values described in Table 1.
Comparative Examples 8 to 12
[0064] Polishing compositions of Comparative Examples 8 to 12 were
prepared in the same manner as in Example 1 except that colloidal
silica with a smooth surface (primary particle size: 32 nm; and
secondary particle size: 61 nm) was used as silica particles, and
further, the pH was adjusted to each of the values described in
Table 1.
Comparative Examples 13 to 18
[0065] Polishing compositions of Comparative Examples 13 to 18 were
prepared in the same manner as in Example 3 except that colloidal
silica with a smooth surface (primary particle size: 32 nm; and
secondary particle size: 61 nm) was used as silica particles, and
further, the pH was adjusted to each of the values described in
Table 1.
[0066] (CMP Step)
[0067] An SiOC wafer and a silicon nitride wafer were polished
using respective polishing compositions under the following
conditions. Here, a wafer with a size of 300 mm was used for the
SiOC wafer and the silicon nitride wafer. Then, for collecting data
for the polishing speed, the SiOC wafer and the silicon nitride
wafer were cut into a square of 3 cm.times.3 cm.
[0068] (Polishing Conditions)
[0069] Polishing apparatus: EJ-380IN-CH manufactured by Engis Japan
Corporation
[0070] Polishing pad: IC1010 manufactured by The Dow Chemical
Company
[0071] Polishing pressure: 1.4 psi (1 psi=6894.76 Pa, the same
applies hereinafter)
[0072] Number of rotations of polishing pad: 100 rpm
[0073] Supply of polishing composition: Discard after single
use
[0074] Amount of polishing composition supplied: 100 mL/min
[0075] Polishing time: 60 seconds
[0076] Specifically, polishing was performed by the following
procedures:
[0077] 1. A polishing pad was subjected to flushing with deionized
water (DIW).
[0078] 2. The DIW was continuously flushed, and the conditioning of
the polishing pad was started at a rotation speed of 100 rpm for 20
seconds by diamond conditioning.
[0079] 3. A polishing composition was dropped onto the center of
the polishing pad for 30 seconds (during which the polishing pad is
rotated), and the polishing composition was allowed to be uniformly
dispersed on the polishing pad.
[0080] 4. An SiOC wafer or a silicon nitride wafer was placed on a
wafer carrier, and the carrier was set on the polishing pad.
[0081] 5. The start button of the polishing apparatus was turned
on, the polishing pad was then accelerated to a rotation speed of
100 rpm, and polishing was performed.
[0082] 6. The wafer was removed from the polishing apparatus, and
then washed with DIW and dried in dry air.
[0083] (Evaluation of Polishing Selection Ratio)
[0084] Firstly, the polishing speed was determined for respective
objects to be polished after the polishing by using the following
Equation 1. The evaluation results are shown in Table 1.
[ Equation 1 ] Polishing speed ( / min ) = Thickness of substrate
before polishing ( ) - Thickness of substrate after polishing ( )
Polishing time ( min ) Equation 1 ##EQU00001##
[0085] Further, in Examples, evaluation was performed by using each
of the SiOC wafer and silicon nitride wafer. However, it is
presumed that, in a case where a wafer (substrate) containing both
SiOC and silicon nitride, or the like is used, a result equivalent
to the above can also be obtained.
[0086] Then, the polishing selection ratio of the SiOC wafer and
the silicon nitride wafer was determined. From the viewpoint of
solving the problems of the present invention, the polishing
selection ratio (SiOC/SiN) is preferably 15 or more.
TABLE-US-00001 TABLE 1 Surface Polishing morphology pH ratio
Selection of silica Coupling adjusting [.ANG./min.] ratio particle
agent agent pH SiOC SiN SiOC/SiN Example 1 Spinous shape -- Nitric
acid 2.7 1204 56 21.6 Example 2 Spinous shape -- Nitric acid 3.4
1586 67 23.5 Example 3 Spinous shape APTES Nitric acid 2.6 781 37
21.2 Example 4 Spinous shape APTES Nitric acid 2.9 1191 39 30.4
Example 5 Spinous shape APTES Nitric acid 3.2 1602 39 40.9 Example
6 Spinous shape APTES Nitric acid 3.4 1905 39 48.4 Example 7
Spinous shape APTES Nitric acid 3.6 2135 45 47.9 Example 8 Spinous
shape APTES Nitric acid 3.9 1837 92 19.9 Comparative Spinous shape
-- Nitric acid 5.0 305 370 0.8 Example 1 Comparative Spinous shape
APTES Nitric acid 5.2 282 276 1.0 Example 2 Comparative Spinous
shape APTES Nitric acid 6.3 205 160 1.3 Example 3 Comparative
Spinous shape APTES Nitric acid 7.2 133 36 3.7 Example 4
Comparative Spinous shape APTES NH.sub.4OH 9.2 18 2 11.5 Example 5
Comparative Spinous shape APTES NH.sub.4OH 10.1 62 11 5.5 Example 6
Comparative Spinous shape APTES NH.sub.4OH 11.0 74 16 4.6 Example 7
Comparative Smooth -- Nitric acid 1.5 209 150 1.4 Example 8
Comparative Smooth -- Nitric acid 2.7 329 45 7.3 Example 9
Comparative Smooth -- Nitric acid 3.5 401 75 5.3 Example 10
Comparative Smooth -- Nitric acid 4.1 332 292 1.1 Example 11
Comparative Smooth -- Nitric acid 6.1 75 195 0.4 Example 12
Comparative Smooth APTES Acetic acid 2.4 245 30 8.2 Example 13
Comparative Smooth APTES Acetic acid 3.4 179 20 9.0 Example 14
Comparative Smooth APTES Acetic acid 4.4 531 80 6.6 Example 15
Comparative Smooth APTES Acetic acid 5.4 182 107 1.7 Example 16
Comparative Smooth APTES Acetic acid 6.4 51 56 0.9 Example 17
Comparative Smooth APTES Acetic acid 7.4 37 20 1.9 Example 18
[0087] From the results of Table 1, it was found that, in Examples
1 to 8 in which the polishing compositions of the present invention
were used, the polishing speed of SiOC relative to the polishing
speed of silicon nitride (SiOC/SiN selection ratio) was
sufficiently high. Among these Examples, from the comparison of
Examples 2 and 6, it was found that, in a case where spinous silica
particles modified with cation were used, a more excellent
selection ratio was obtained. Meanwhile, in Comparative Examples 1
to 7 in which the pH was 5 or more, spinous silica particles were
used, but the SiOC/SiN selection ratio was low. Further, in
Comparative Examples 8 to 18, since spinous silica particles were
not used, the SiOC/SiN selection ratio was low regardless of the
value of the pH.
* * * * *